I had a look at the video. The camera moves away from the overflow riser on the flush valve when the water is less than 1/4" from the top and the thing is still filling; a careful listen seems to suggest that the tank water level is rising higher than the top of the overflow riser and that water is overflowing into the riser before the valve shuts off. It's as if the water has become high enough to trigger a shutoff, but the valve takes a moment to respond, resulting in water down the overflow tube. Is that what's happening?

If cleaning the filter doesn't solve the groan or, more importantly, the overflow, then a new fill valve is in order. It's a very easy install -- water off, place bucket under bottom of fill valve, flush, disconnect water supply hose from bottom of fill valve, disconnect refill hose from fill valve and overflow riser, hand-unscrew mounting nut for fill valve, pull old valve out, unlock new Korky 528MP (or 528T), place in toilet, adjust valve height so water level mark on valve is 1/2" below top of overflow riser, twist to lock valve in place, tighten mounting nut (beveled side up), reattach refill tube, reattach supply line, turn on water, congratulate self.

If you installed the toilet yourself, this part is easy.

When you get your new fill valve, you want the 528MP [silver top] (which you will likely run with the refill all the way open: that's 40 percent refill, which is what the GMax valve is), or the 528T [blue top] (which is fixed at 40 percent refill). Don't let anyone sell you the white-top 528, because that won't refill your bowl enough (20% refill -- old industry standard). If/when you have this kind of problem with the 528 years from now, it can be fixed by cleaning the parts of the valve and if that doesn't work, by swapping out a little cap in the valve with a readily-avalable $3 part that contains the water-control diaphragm. Even easier than changing the whole valve.

Korky has a video on how to change the valve here: Korky Installation Video Don't worry about the fact that they use a white-capped valve in the video; all the 528s are basically the same, except that some just have different refill ratios. (I did notice that the video says to turn off the water by turning the valve handle clockwise, which is correct, except that while saying this, they turn the handle counterclockwise. Doh!)

@wjcandee - Wow, thanks for the thorough walk through. I had adjusted the water level many years ago as the bowl did not seem to fill well and (without sanigloss) i wanted a bit more water in there. I know when I adjusted it, the water level was definitely NOT flowing into the riser - but you are right - I notice it does flow in there for a few seconds.

Have fiddled with that but it doesn't seem to want to stop overflowing. Is there anything wrong with it flowing into the riser? It does keep a good level of water in the bowl, which I like.

I am from Edmonton, Alberta and the City water here is quite hard. I see a lot of hard water deposits built up so will clean that first and see what happens.

For what it's worth, the bowl is designed to hold a certain amount of water. If any more water than that flows into the bowl, it may initially appear to raise the level a bit, but the level will settle back to the bowl's design. 40% refill ratio combined with a fill of the tank to the right height on the gmax flush should fill or slightly-overfill the bowl. (One of the ways they reduce to 1.28 from 1.6 is to try to eliminate overfilling. Because each flush doesn't empty the bowl exactly the same way, there was a tendency on old toilets to just overfill in order to make sure there was enough water. Hence on many old toilets, the bowl will refill and then more water will keep running into it for 15-20 seconds on most flushes, but on others it will only overfill for 5 seconds. Even on the Gmax there is occasionally a little overfilling on some flushes, but not on most.)

The tank water should never be running down the overflow riser (of course, the toilet will send water down that riser from the refill hose). That's because if a properly-functioning valve doesn't shut off by the time the water level gets to the top of the overflow riser (hint: "overflow"), the water in the tank isn't likely to rise much higher, and then there will be nothing to signal the valve to shut off. The issue in your toilet is that I can plainly see the water exceed the height on the fill valve that would normally cause it to close (shut off), but the valve delays shutting off. Why? Dunno. In any event, that extra water isn't going to give you a higher level of water in the bowl after the toilet has settled for a minute or so; it's just going to go down the drain.

It might be worth taking that valve out and washing it off, besides just cleaning the filter. It may do no good whatsoever (it does do good with the Korky valve, but maybe not this one), but it can't hurt. Right now, you seem to have a valve that's just a smidge away from not closing at all, which would give you a runaway toilet that hopefully won't overflow into the room, depending upon how well the overflow riser can capture the water running into the toilet from a valve that won't close. If it were I, just because I like fooling with this stuff, I would replace it.

In Canada, Korky products are distributed by Lyncar (800-263-7011). According to them, in Edmonton, you can get the 528MP at any of the following: AMRE Supply (2 locations: Downtown and South), B.A. Robinson (Robinson Lighting & Bath Center), Bartle & Gibson, Best Plumbing & Lighting Design Center (a Toto dealer, too, but get the Korky valve b/c it's cheaper and a better design than the one you have), and any one of the branches of Emco Alberta. I would call over before going to make sure (1) they have it in stock and (2) they will sell it retail, as some of these guys may be wholesalers.